The herein invention refers to a device for digging narrow trenches and laying inside them different sorts of prefabricated piping composed of short, straight and rigid sections, which are tongued and grooved to join together. Both the digging of the trench and the laying of the piping or pipes, as well as the compacting and final smoothing of the excavated material are carried out in a single operation and at a fair speed. The device of the invention has been developed in order to lay auxiliary piping for high speed railways, but it may also be used for electrical and communications cables in built-up areas, for irrigation canals, and so forth.
Devices for digging narrow ditches with the aid of disc trenchers are well-known. Thus, in the same applicant""s document ES 8703560 a disc trencher is specified which is specially adapted to dig narrow trenches in compacted ground, using a cutting disc whose periphery is made up of a number of replaceable hard metal spikes, while the depth of cut may be regulated due to the fact that the chassis rests on the ground through the mediation of a wheel of adjustable height.
In turn the same applicant""s document ES 2027503 specifies a device which, on the basis of the trencher specified in the former document, embodies means to support a cable reel and an oscillating guide tube for laying cable on the floor of the trench, thus permitting the digging of the trench and the laying of the cable in the same uninterrupted action.
However, all these devices are intended for the digging of trenches and the subsequent laying of cables served on reels, but they are not viable for the laying of prefabricated concrete pipes embodied in short sections and, naturally, completely rigid.
The problem that arises is that once the trench has been dug, steps have to be taken to ensure that no earth falls back into the trench as this would affect the regularity of the supports for the piping on the floor of the trench and, more importantly, the correct fitting and levelling of each pipe with the next one.
Document U.S. Pat. No. 5,707,175 specifies a device composed of a trench digger allied to a feeder-loader which is adapted for the laying of tongued and grooved piping. Its objective is to carry out more or less continuously the digging of the trench and the laying of the pipes. To this end the feeder-loader contains a certain number of pipe sections stacked vertically. A mechanical retainer releases at the opportune moment the lower pipe section and it is then the job of a hydraulic piston to fit it into the groove, greater in diameter, of the last pipe section to have been laid in the trench. Although such a solution solves the problems of lowering the pipe section onto the floor of the trench without the risk of any crumbling of the trench""s walls and ensures the coupling and watertightness of the pipeline, it also entails a basically interrupted operation, that is to say lowering and pushing, as well as causing severe difficulties when it comes to regulating the digger""s speed of advance and to aligning the successive pipe sections. As a result, the device is liable to breakdowns and interruptions.
The device of the invention has been conceived in order to provide a fully satisfactory solution to this problem. To this end it has been projected to mount on one and the same vehicle the disc trencher, the means that enable the levelling and containing of the excavated earth, and, in particular, a sweeping box which, positioned behind the trencher, enables the earth to be levelled and contained by its exterior while the successive pipe sections, joined together and subjected to a thrust that allows a continuous pipeline to be formed, drop down in its interior. It is thus possible to achieve the digging of the trench of exact dimensions in any type of ground, whether compact or loose, while the earth at the sides is prevented from falling to the floor of the trench and causing problems for the support of the pipeline; meanwhile, the exceedingly fine finish of the digging on the floor of the trench constitutes an excellent bed on which to rest the rigid pipe sections over the ground. Moreover, the pipe sections are interlocked at their front end and deposited in the sweeper box with the aid of a certain longitudinal thrust, thereby behaving like an articulated polygon in the face of the small deviations in inclination to which they are subject.
The device which is object of the invention comprises a vehicle of traction which incorporates a disc trencher at its rear with a breadth of cut slightly greater than the breadth of the pipe sections. It attains a working depth adequate to the height of the pipe sections. As the pipe sections must lie at the level of the ground, the device incorporates a support wheel on which the trencher""s chassis rests and which, since its height may be regulated, maintains the desired cutting depth.
At the rear of the disc trencher and horizontally to it, a roller-feeder is attached by one of its ends while its other end is supported on wheels. The pipe sections are deposited manually or with the aid of a forklift or excavator-loader equipped with a hydraulic grab. The roller-feeder is slightly inclined so that the pipe sections are moved horizontally to their longitudinal axis until they drop into a roller-pusher. This roller-pusher is aligned in the direction of movement and is also slightly inclined in such a way that the degree of inclination diminishes progressively to a minimal value, which is very close to the horizontal.
The pipe sections are trapped against the roller-pusher by a number of pneumatic drive wheels which transmit to them by friction a force that pushes the sections against each other and thus forces them to enter the trench. The speed at which the drive wheels turn is variable and regulated by means of a tachometer in the drive motor itself, which is what supplies them with their spinning motion; thus the speed at which they turn may be adapted to the speed at which the vehicle of traction advances, while it is anticipated that there will be some slippage between the drive wheels and the pipe sections, that is to say, the pneumatic wheels tend to displace the pipe sections at a speed faster than that of the device""s movement over the ground since the maximum thrust effort absorbed by the pipe sections is limited by the coefficient of wheel/pipe section friction.
The sweeper box has a guideable blade backed laterally and at the same level as the ground in order to distribute the excavated material leaving most part of it in an excavation slope but reserving a small quantity for filling in the lateral grooves between the pipe sections and the trench walls. It comprises in its rear part two levelling blades for extending the excavated material and filling in the grooves between the pipe sections and the trench, as well as compacting rollers which compact and plane the excavated material used for filling in the grooves, by pressing it downwards and against the external walls of the pipe sections.
Although the device that has just been specified has managed to triple the speed of pipe laying and, at the same time, to halve the number of workers required in comparison with the pre-existing art, various problems have been detected which cause deterioration to the edges of the pipe sections as well as sporadic interruptions in the laying device.
In this regard, a first source of difficulty lies in the fact that the swinging stopper used to feed the pipe sections horizontally permits them to pass in compact groups until the first one comes into contact with the roller-pusher. As a result of this, the first pipe section is trapped laterally by the weight of the succeeding sections and is subjected to a friction of sufficient magnitude to cause its movement to be stopped and to prevent it from reaching the first thrust wheel. The solution proposed consists in substituting the swinging stopper with a rotating feeder, the movement of which is stepped in such a way that it only releases one pipe section at a time.
A second problem has been found to lie in the defective lateral alignment of the successive pipe sections once they have been trapped in the roller-pusher. It has been observed that if the pipe sections have sufficient freedom to move transversally in the roller-pusher, the tongues and grooves at their ends may not coincide and, since the whole line of pipe sections is subjected to a strong longitudinal thrust, the edges of the flanges that constitute the tongues and grooves may suffer some deterioration. The solution proposed lies in the fact that the drive wheels are of a width that coincides substantially with the central channel of the pipe-sections and this ensures that they are guided perfectly and the tongues and grooves of successive pipe sections are coupled together smoothly, without any interference.
A third problem was detected which has to do with the fact that, as the pipe sections are lowered, they describe a straight trajectory forming a slight angle with the ground as they are pushed by the device of the invention; but that once they have been deposited on the floor of the trench they logically adopt the same alignment as the ground. The upshot of this is that when they leave the device, the successive pipe sections tend to rest on each other at their upper side, as a result of which this area may suffer small breakages which, although they do not affect the good working order of the pipeline, contribute to a deterioration in its visual appearance. The solution proposed consists in inserting between successive pipe sections separators of some soft material that will absorb the shocks and prevent any direct contact between the upper parts of successive pipe sections.
In order to bring to a close the foregoing specification and to assist in the better understanding of the invention, a detailed description of a preferred embodiment will be given on the basis of a set of drawings that are attached to this specification, and where, merely for the purposes of guidance and in no way limiting, the following has been represented: